The first time I ever photographed a caddisfly, I posted it to a butterfly and moth forum and asked for help with the identification. They were very kind, but I was very embarrassed. I feel better about it now, though, because a 2008 DNA study established that the Trichoptera (caddisflies) and Lepidoptera (butterflies and moths) are sister orders, being more closely related to each other than they are to other kinds of insects such as flies.
The name ‘Trichoptera’ refers to the bristly wings of the caddisflies – this being the most obvious difference between them and the scaly-winged Lepidoptera. One important similarity though is that members of both orders can spin silk. Caddis fly larvae, which are almost all aquatic*, create protective cases for themselves from stones, sand, leaves and twigs, bound together with silk secreted from glands around the mouth. In some species these cases are fixed shelters, but in others such as the Cinnamon Sedges they’re portable, allowing the larvae to move between feeding sites. The species which create these portable shelters tend to feed on detritus such as decaying plant matter.
As is the case with other insects that develop in water but emerge to breed, most of a caddisfly’s life is spent underwater. After passing through five to seven larval instars, it will fix its portable shelter to something stable, seal the ends against predators, and pupate; then emerge, swim to the surface, and immediately undergo one final moult to become a fully-winged adult. In many species the adults cannot feed, and live at best a few weeks, though some are known to take nectar. They tend to be nocturnal, resting in shelter during the day, though I found this one out in plain sight on one of the dogwoods in the wild garden. Ecologically, caddisflies are regarded as a bioindicator of good water quality because they’re sensitive to pollution, and I take the fact that I seem to be finding them in the garden in steadily increasing numbers as an endorsement of the condition of our ponds.
Many caddisflies are difficult to identify as adults (though the protective cases created by their larvae are species-specific and distinctive), but this is one of the easier ones. The pale half-moon with a dark edging on the rear margin of the wing makes it Limnephilus lunatus, which is a common and widespread species of streams, ponds, lakes, and marshes. It’s 10-15mm in length, and can be seen from May to November.
*One very notable local exception to the aquatic larvae “rule” is the species Enoicyla pusilla, commonly called the Land Caddis, whose larvae live in leaf litter on damp forest floors. In the UK this species is pretty much confined to the Wyre Forest in Worcestershire.
